FreedomYachts.org

OK smart people, I have a mystery wrapped in an enigma. When I fill my water tank (standard F30 plastic under stbd settee) as the tank fills to about 2/3 full it begins to develop pressure, a lot of pressure, enough to begin ripping screws out of the over tank cover and the front of the settee base. I realize there is an overflow tube in the upper part of the tank and I am able to blow back through this when the pressurization begins but I do not get the expected flow from the tube. I am obviously missing some basic science related to air and water pressures. Help!!

If I understand correctly and water is not coming out the vent line with al that pressure then the line must be clogged. Manuually blowing into it you probably can't tell because of the length of the tubing ad volume of air you would need to really check it. You could try an air compressor. Or just run a wire through it.

Mike,
the vent line must be clogged or restricted. If you use compressed air to blow down it, make sure your filler cap is removed and taps on to relieve any pressure in the tank. Even a small amount of pressure can do a lot of damage as you have seen. It may also be that the vent is too small for the rate at which the tank is being filled. I remember years ago filling a new tank I had fitted in an old launch. I had from memory something like a 1 1/4" fill line and two 2 3/8 to 1/2" vents. I reasoned (in error as it turned out) that air would flow out more easily than the diesel would flow in. Once the tank was about half full there was enough pressure to force the fuel back up the fill line, making an awful mess. as I stopped pumping I could hear the air hissing out of the vent lines. The answer in this case was to fill the tank more slowly to allow the vents to relieve the pressure.

Regards,

Mike, you might want to check if your tank vent hose doesn't extend too low inside the tank. If it is, you can blow back air into the tank, but air cannot escape when the tank is filled. Perhaps the longitudinal trim of your boat is different now, so that the vent is not at the highest point in the tank anymore.

Thank for the ideas, suggestions everyone. I will go down to the boat a get serious about investigating clogs and location of vent. Freedom Yachts, of course, made it a diabolical effort to view all the tank gozintas and gozoutas. Things are very tight all around the tank and its hard as heck to see the business end of the tank which is butted up against the aft settee/chart table bulkhead.

Mike -

I'm redoing the plumbing on my F-30 now.

I took a hole saw and made a 4" hole in that bulkhead to get at the plumbing connections and re-route the outlet. Then I coated the cut wood edges with epoxy and covered the hole with a SS louver.

My vent goes up behind the electrical panel and then is routed back down alongside the water tank to vent into the bilge. I'd like to figure out a way to vent it into the galley sink (of course it is on the other side of the boat.